Worker protection standards are based upon single exposures and do not account for the constellation of exposures frequently encountered by nuclear weapons production and site clean-up workers or by the growing number of hazardous waste workers. Workers may encounter asbestos fibers during building decontamination and demolition and be concomitantly exposed to radiation. Both hazards cause pulmonary fibrosis, a chronic condition. The health effects of toxicant mixtures and chronic respiratory disease are each priority areas for the National Occupational Research Agenda. The main focus of this study is to determine whether concomitant radiation exposure increases the fibrogenic effect of asbestos as demonstrated by an increase in ILO opacity profusion category on chest radiographs, or spirometry based case definitions of pulmonary fibrosis. Using a cohort design, 300 asbestos exposed nuclear workers will be divided into very low and high radiation dose groups based upon personal dosimetry records and then compared for evidence and degree of pulmonary fibrosis. The following hypotheses will be addressed Hypothesis 1. Radiation dose increases the risk of pulmonary fibrosis in workers exposed to asbestos. Hypothesis 2. Exposures at ages greater than 45 years confer a greater risk than exposures earlier ages. Hypothesis 3. Internal lung dose estimates are a better predictor of pulmonary fibrosis effect than external film badge dosimetry. Hypothesis 4. Chronic Low Energy Transfer (LET) radiation is more effective than brief exposures to high energy radiation in enhancing the fibrotic effects of asbestos. Answers to these questions should improve the risk profiling of former USDOE workers as well as those involved in future remediation of radiation and asbestos contaminated sites.